The present invention relates to a system for non-intrusively and wirelessly monitoring pressure, temperature and/or other parameters in the casing annuli of a subsea hydrocarbon production system. More specifically, the invention provides an apparatus and method for monitoring the parameters in the casing annuli using a near-field magnetic or an inductive through-wall communications system to communicate with one or more sensing packages located in corresponding casing annuli.
Sustained Casinghead Pressure (SCP) is a pressure build-up within the casing annuli of a subsea hydrocarbon production system which is due solely to temperature fluctuations. The need to monitor SCP has been identified by the Minerals Management Service (MMS) of the United States Department of the Interior. However, this requirement has been waived for certain subsea hydrocarbon production systems due to other regulatory prohibitions against body penetrations in high pressure wellhead housings.
In addition to regulatory demands for the development of technology for the non-invasive monitoring of casing annuli, operators are interested in such monitoring in order to mitigate the risks to personnel, equipment and system availability which may be caused by working on equipment in an unknown pressure condition or incidents such as the collapse of production tubing due to pressure in the B annulus, i.e., the production casing annulus. Operators have experienced failures on non-High Pressure High Temperature (“HPHT”) wells due to excessive pressure in the B annulus, and the risks of annulus pressure build-up and subsequent damage are more acute in HPHT wells due to thermal expansion of trapped fluid within the casing annuli.